Bundling of cellulose microfibrils in native and polyethylene glycol-containing wood cell walls revealed by small-angle neutron scattering

Abstract

Wood and other plant-based resources provide abundant, renewable raw materials for a variety of applications. Nevertheless, their utilization would greatly benefit from more efficient and accurate methods to characterize the detailed nanoscale architecture of plant cell walls. Non-invasive techniques such as neutron and X-ray scattering hold a promise for elucidating the hierarchical cell wall structure and any changes in its morphology, but their use is hindered by challenges in interpreting the experimental data. We used small-angle neutron scattering in combination with contrast variation by poly(ethylene glycol) (PEG) to identify the scattering contribution from cellulose microfibril bundles in native wood cell walls. Using this method, mean diameters for the microfibril bundles from 12 to 19 nm were determined, without the necessity of cutting, drying or freezing the cell wall. The packing distance of the individual microfibrils inside the bundles can be obtained from the same data. This finding opens up possibilities for further utilization of small-angle scattering in characterizing the plant cell wall nanostructure and its response to chemical, physical and biological modifications or even in situ treatments. Moreover, our results give new insights into the interaction between PEG and the wood nanostructure, which may be helpful for preservation of archaeological woods.

Water-accessibility of interfibrillar spaces in spruce wood cell walls

“…Nevertheless, the fitting results (Table 1) indicated no difference in the nanostructural parameters of the samples dried from H 2 O and D 2 O. Both followed the previously reported trends of decreasing interfibrillar distance (Penttila ¨et al 2019) and microfibril bundle diameter (Penttila ¨et al 2020a) as a result of drying. The former condition corresponds to the matching point of crystalline cellulose, at which the contrast between cellulose microfibrils and the surrounding water-accessible matrix is decreased to minimum and the contribution from the microfibrils disappeares from the data (Figs.…”

“…The cylinder centre points are separated by distance a and the paracrystalline distortion is described by Da. The contribution represented by the second term (with scaling factor B) in SANS data from wood has been linked to the aggregation of microfibrils, and it allows determining the diameter of microfibril bundles as 2 ffiffi ffi 2 p =r (Penttila ¨et al 2020a). The third term (with scaling factor C) corresponds to power-law scattering by large pores and cell lumina (Jakob et al 1996;Nishiyama et al 2014).…”

“…At the same time, the analysis of small-angle scattering data from wood samples is facilitated by the recently developed WoodSAS model (Penttila ¨et al 2019). This model can be used to determine the diameter of cellulose microfibrils and their packing distance under various moisture conditions (Penttila ¨et al 2020b), and in the case of SANS, the diameter of microfibril bundles can also be obtained (Penttila ¨et al 2020a).…”

Chemical Changes of Wood Treated with Caffeine

“…On the other hand, it is interesting that the calculated molecular size of caffeine is 0.78 nm in length. As is known, the secondary cell wall alone has a lateral thickness of 2 to 3 nm [60]. The exact morphology is not yet fully explained, but we can initially conclude that the penetration of caffeine into the cell wall cannot progress through spherical blockades.…”

Deswelling of microfibril bundles in drying wood studied by small-angle neutron scattering and molecular dynamics

“…Due to poor data for dry wood, any values yielded by the analysis are merely approximate and the values of a and R for dry wood had to be fixed to 34.5 Å and 11 Å respectively, for the fitting to provide meaningful results. Regardless, there was a clear increase in the value of r from 0.019 to 0.026 Å -1 , roughly corresponding to the bundle diameter shrinking from 15 to 11 nm (Penttilä et al 2020a). While the exact value of the shrinking may not be accurate, evidence for shrinking bundles was still there.…”